Learn English – differentiating between correlation and a temporal relationship

The construction The reason is because X has been upsetting pedants for about four generations now. Don't worry about it: it is a fixed phrase and beyond grammatical niggling. Millions of people use it every day, in every register, and writers of the very first rank have used it for at least four hundred years.

If you want a reasoned discussion from a recognized expert you may consult the blog Motivated Grammar written by Gabe Doyle of the Language and Cognition Lab at Stanford University:

A mild amount of redundancy improves the likelihood of the message being transmitted correctly. The problem is when there’s too much redundancy, slowing down the rate of communication. (A common problem in children’s conversations, for instance, or a boring person’s stories.) Using because instead of that here doesn’t slow anything down, though — aside from the couple hundred milliseconds the additional syllable might cost the speaker — so I’m pretty unsympathetic to this complaint as well.

But I beg you, abandon the effort to understand the use of words by replacing them with their etymologies and dictionary definitions. That's not how any language works; it's a dead end for a learner.